1. Field of the Invention
The present invention relates in general to a fluid-filled elastic mounting structure suitably used as a mount to mount for example an engine of a motor vehicle, and more particularly to such a fluid-filled mounting structure capable of effectively damping and isolating input vibrations in a wider frequency range than the known structure.
2. Discussion of the Prior Art
An elastic mounting structure such as an engine mount for an automotive vehicle is generally required to effectively damp and isolate input vibrations in a wide frequency range, in particular, to effectively damp the vibrations having low frequencies. To meet these requirements, there has been proposed a so-called fluid-filled elastic mount comprising: (a) first support means and second support means which are spaced apart from each other in a load-receiving direction in which a vibrational load is applied to the elastic mount; (b) an elastic body interposed between the first and second support means, for elastic connection of the first and second support means; (c) a closure member secured to the second support means and cooperating with at least the elastic body to define a fluid chamber filled with a non-compressible fluid, the closure member including a flexible portion; (d) partition means for dividing the fluid chamber into a pressure-receiving chamber formed on the side of the first support means, and an equilibrium chamber formed on the side of the second support means, (e) means for defining a restricted passage for restricted fluid communication between the pressure-receiving chamber and the equilibrium chamber.
In the known fluid-filled elastic mount constructed as described above, vibrations applied to the mount cause the non-compressible fluid to flow between the pressure-receiving chamber and the equilibrium chamber, through the restricted passage, so that the elastic mount can effectively damp the input vibrations in a specific frequency range which is determined by the configuration and dimensions of the restricted passage. Usually, the restricted passage is tuned to a certain frequency in a low frequency range so that the low frequency vibrations can be effectively damped due to restricted fluid flows through the restricted passage.
Although the known fluid-filled elastic mount can effectively damp the low frequency vibrations by the restricted passage, it cannot always sufficiently damp and isolate the input vibrations in other frequency ranges, in particular, in a higher frequency range than the frequency range determined by the restricted passage. More specifically, where the known elasic mount is subjected to the higher frequency vibrations, the fluid is less likely to flow through the restricted passage, leading to reduced damping or isolating capability of the elasic mount.
In view of the above inconvenience encounterd on the known elasic mount, there has also been proposed a fluid-filled elastic mount constructed as described above, further comprising (g) a movable member which is supported deformably or displaceably in a direction to absorb a pressure difference between the pressure-receiving and equilibrium chambers. According to the thus constructed elastic mount, the input vibrations in a specific frequency range can be effectively isolated, based on deformation or displacement of the movable member corresponding to the amount of the above-described pressure difference. Since the specific frequency range which is determined by the size and configuration of the movable member is set to a relatively high frequency range, the elastic mount can exhibit excellent isolating characteristic for the relatively high frequency vibrations.
Consequently, the elastic mount as described just above can effectively damp and isolate the input vibrations of two different frequency ranges, that is, the low frequency range determined by the restricted passage and the relatively high frequency range determined by the movable member. However, the known elasic mount cannot demonstrate excellent isolating characteristics for the vibrations in a frequency range which is higher than the specific frequency range determined by the movable member. More specifically, the elastic mount having the movable member can isolate the input vibrations whose frequencies are at most 150-200 Hz, but does not have sufficient isolating capability against the vibrations in a higher frequency range than the above-indicated range of 150-200 Hz.